Within　density　function　theory　under　the　generalized　gradient　approximation,　for　ideal　Co2MnSi/GaAs　(001)　and　(110)　multilayer　structures,　the　CoSi-AsGa　interfaces　are　found　to　be　half-metallic.　While　the　most　stable　(110)　CoSi-GeGe　interface,　for　the　ideal　Co2MnSi/Ge　multilayer　systems,　is　near　half-metallic.　Given　the　atomic　disorder　in　the　Co2MnSi/GaAs　(001)　((110))　multilayer　systems　with　the　CoSi-AsGa　interface,　Co　anti-site　defect　is　more　readily　presented　at　the　(001)　((110))　interface.　These　results　show　that　the　low　tunneling　magnetoresistance　ratio　or　spin　injection　measured　in　Co2MnSi/GaAs　(001)　(or　(110))　tunnel　junction　in　some　experiments　may　be　relevant　to　the　interfaced　Co　anti-site　defect　as　well　as　interfacial　structure.　(c)　2011　Elsevier　B.V.　All　rights　reserved.